Problem: $-\dfrac{8}{10} + \dfrac{2}{4} = {?}$
Answer: $ = - {\dfrac{8 \times 2}{10 \times 2}} + {\dfrac{2 \times 5}{4 \times 5}} $ $ = - {\dfrac{16}{20}} + {\dfrac{10}{20}} $ $ = - \dfrac{{16} + {10}}{20} $ $ = -\dfrac{6}{20}$